In general, aquatic creatures living under water, such as barnacles, sea squirts, serpula, mytilus galloprovincialis, freshwater shellfish, lagoon bugyul body, visible bluish, greener and so on, adhere to and live in a surface of the body of a ship, which does various damage to the ship.
For example, aquatic creatures adhered to the ship body may increase frictional resistance to seawater, thereby decreasing a sailing speed of the ship and increasing fuel consumption, which is at an economic disadvantage.
Conventionally, a cleaning work by a worker of moving a ship to be cleaned to a land dock and stripping off attachments of the wall of the ship by jetting water with a high pressure hose has been generally used. Since this method requires a preparation procedure to move the ship to the dock, there is a disadvantage that long cleaning time is taken and many workers are mobilized.
A diver may clean the bottom of the ship under water, without moving the ship. However, even for a diver skilled at underwater work environments, it takes a long time to clean a wide range of ship body and the level of difficulty in the cleaning work increases due to poor visibility.
In order to avoid the problem that cleaning the bottom of the ship by a worker is difficult to remove attachments efficiently and requires many workers, there has been proposed a method of applying paints mixed with toxic material in order to prevent marine creatures from adhering and parasitizing in the surface of a ship.
However, the proposed method causes other problems of seawater pollution and detrimental effects on other marine creatures to destroy the aquatic ecosystems and is therefore forbidden by international organizations. In addition, when the toxicity decreases after lapse of certain time, paints should be again applied after cleaning.
In order to overcome such a problem, there has been proposed a technique that a cleaning robot removes deposits while moving along the wall of a ship under water.
“An underwater robot for cleaning and inspection of the bottom of a ship” disclosed in KR Patent Registration No. 10-0811540 is a propulsive apparatus which moves along the wall of a ship body and cleans the wall using a brush fixed at the underwater robot.
However, this method causes upsizing of cleaning equipment due to a propeller, which results in difficulty in efficient cleaning of the ship bottom having a large curvature, and requires many sensors used to stably move the robot along the wall of the ship body, which results in high costs.
In order to clean the bottom of a ship, it is important to closely attach a cleaning apparatus to the ship bottom. To this end, there has been proposed a method of using a magnetic wheel.
Some cleaning apparatuses using magnetic wheels have no consideration of uniformity of an attachment target surface including the ship bottom.
In this case, if the attachment target surface to which one of the magnetic wheels is attached is lower than the ground, the corresponding magnetic wheel may be detached from the attachment target surface and, accordingly, the overall force with which a cleaning apparatus is attached to the attachment target surface is weakened.
If attachment target surfaces of diagonally arranged magnetic wheels are lower than other attachment target surfaces, the diagonally arranged magnetic wheels are simultaneously separated from the attachment target surfaces. Therefore, since a load is weighted on magnetic wheels diagonally arranged in a different direction or three of four magnetic wheels contact the attachment target surfaces simultaneously and are obliquely attached to the attachment target surfaces, a magnetic force of the magnetic wheels cannot be properly delivered.
In actuality, since the bottoms of most ferromagnetic bodies as attachment target surfaces are not flat, there is a disadvantage in that a design should be made in preparation for non-attachment of magnetic wheels to attachment target surfaces. In addition, more than four magnetic wheels are difficult to be mounted due to characteristics of the magnetic wheels that an adsorptive force is rapidly decreased if the magnetic wheels are separated from the attachment target surfaces.
On the other hand, when magnetic wheels are attached to floors, walls, ceilings and so on formed of a ferromagnetic body, an external force exerts to separate the magnetic wheels rather than to press the magnetic wheels.
Even if the volume of a magnet is increased twice, a magnetic force is increased less than twice. Therefore, the size of the magnet cannot be blindly increased. Therefore, in order to increase the adsorptive force of the magnetic wheels, it is more effective to use a number of magnetic wheels.
In this case, providing springs in individual magnetic wheels may be considered. For example, in a case of using tension springs, when the forefront magnetic wheel of a plurality of magnetic wheels is applied with a force and is attracted, there differs in forces applied to magnetic wheels arranged in the rear side depending on an elongation percentage of the tension springs. That is, the magnetic wheel located in the forefront shares the largest force and the magnetic wheel located in the rearmost shares the smallest. This is inefficient because the respective magnetic wheels do not evenly share an adsorptive force against an external force.
The above description is only provided as a background to assist in understandings of the present invention but is not intended to elucidate the technique known in the art to which the present invention belongs.